1. Field of the Invention
This invention relates to conveyors for moving load units, such as loaded pallets or slip sheets, from a first location to a second location, and in particular to such a conveyor which acts to accumulate the load units proximate the second location for subsequent removal from the conveyor.
2. Description of the Related Art
Conveyors of various kinds are generally used in industry to move load units from one location to another. An accumulating conveyor differs from an ordinary transfer conveyor in that it has the ability to retain load units and store them until they can be removed as needed. One well known type of accumulating conveyor generally comprises a track upon which load units are placed and a lifting mechanism for lifting the load units relative to the track. The load units are indexed forward by sequentially lifting a load unit off of the track, moving it forward, and then setting it back down on the track. The lifting mechanism is then moved rearwardly, and the process is repeated.
For example, Milazzo, U.S. Pat. No. 3,322,259, discloses (as an alternative embodiment) an Accumulating Pallet Conveyor having a horizontal track with parallel side rails and a carriage with multiple lifting plates or platforms which are reciprocally moveable, with the carriage, along the track by a pneumatic cylinder. The carriage rolls on top of a plurality of rollers which are secured to the side rails. An air bladder is positioned beneath the lifting platform and can be inflated and deflated to raise and lower the lifting platform relative to the carriage. When the platform is lowered, any load unit positioned above the carriage will rest on the track side rails. When the platform is raised the load unit will be lifted clear of the side rails and supported by the carriage. The carriage is reciprocally moveable along the track by a pneumatic cylinder.
Inflation and deflation of the bladders in the Milazzo conveyor is controlled by a pneumatic system which includes a normally closed limit switch mounted on the first platform which actuates a solenoid valve controlling airflow through a main line. Each of the bladders is connected to the main line through a respective normally open sensor valve which is mounted in association with the next lifting plate ahead of the lifting plate under which the bladder is mounted. Note that the sensor valves are not mounted directly to the lifting platforms, therefore they only detect the presence of a load unit that is resting on the side rails, not ones that are lifted by the bladders. A normally open sensor valve mounted to the track in the unload position controls airflow to the bladder under the last lifting platform.
Thus, when a load is placed on the first lifting platform, each bladder will inflate unless there is a load unit sitting on the side rails above the next lifting platform. As the bladders inflate, the respective load units are lifted off of the side rails. Any of the remaining bladders which are controlled by sensor valves of the lifting platforms with raised loads will also inflate once the load units clear the side rails. In effect, this means that each of the bladders will eventually inflate unless all of the remaining positions nearer to the unloading position are already filled. While this system provides a means of accumulating pallets near the unloading position, it creates an undesirable time delay during the inflation process.
There remains a need for an accumulating pallet conveyor and storage system which is relatively inexpensive to manufacture while still providing for the automatic accumulation of palletized loads.
The present invention comprises a conveyor for advancing load units from a loading position toward an unloading position. The conveyor includes a track having a pair of side rails, each of the which have an upper surface and an inwardly extending flange spaced downwardly from the upper surface. The track defines a plurality of sequential load unit positions, a first of the load unit positions being a loading position proximate a first end of the track, an d a last of the load unit positions being an unloading position proximate a second end of the track.
The conveyor further includes a plurality of interconnected carts which include wheels that ride on the inwardly extending flanges of the track. The number of carts is at least one fewer than the number of load positions. A first one of the carts is located proximate the first end of the track and a last of the, carts is located proximate the second end of the track. Each of the carts is adapted to receive a respective load unit and includes a pair of lifting platforms for raising the respective load unit relative to the track. An air bladder positioned beneath each lifting platform is selectively inflatable and debatable for moving the respective lifting platform between a lowered position wherein the upper surface of the lifting platform is below the upper surface of the track side rails and a raised position wherein the upper surface of the lifting platform is above the upper surface of the track side rails. A load unit positioned on a cart will, therefore, rest on the side rail upper surfaces when the lifting platforms are lowered and be lifted clear of the side rail upper surfaces when the lifting platforms are raised.
A pneumatic cylinder is connected between the track and the carts for reciprocally moving the carts along the track between a home position wherein the first cart is in the loading position and a forward position wherein the last cart is in the unloading position. A pneumatic system controls the cylinder and each pair of bladders so as to advance a load unit from the loading position toward the unloading position by cyclically moving the load unit into the raised position, moving the carts into the forward position, moving the load unit into the lowered position, and moving the carts back into the home position beneath the load unit.
The pneumatic system includes a plurality of sensor cams, one of which is mounted to a lifting platform of each cart. Each sensor cam is operable in response to a load unit being positioned on the respective cart to actuate a respective sensor valve. Similarly, an unloading position sensor is mounted on the track at the unloading position. The unloading position sensor is operable in response to a load unit being positioned in the unloading position to actuate an unloading position sensor valve.
The pneumatic system includes a bladder inflation circuit for selectively inflating the air bladders. Airflow into the bladder inflation circuit is controlled by a bladder inflation valve which is actuated upon the carts arriving in the home position. The bladder inflation circuit includes a first branch which is connected to all of the air bladders. Airflow into the first branch is controlled by the unloading position sensor valve, such that all of the air bladders may be inflated when no load unit is positioned on the track at the unloading position.
A second branch of the bladder inflation circuit is connected in parallel to the first branch. Airflow into the second branch is controlled by the sensor valve on the first cart such that no air will flow into the second branch unless a load unit is positioned on the first cart. The second branch includes a plurality of parallel legs. Airflow through each of the legs is controlled by a respective one of the cart sensor valves. Each of the legs is connected to the pair of air bladders on the cart which is one cart nearer to the first cart than is the cart to which the sensor cam actuating the respective sensor valve is mounted.
The first branch and the second branch are interconnected such that a respective air bladder is not inflatable if load units are positioned at the unloading position and on any of the carts which are nearer to the last cart than the cart on which the respective air bladder is mounted.